1. Field of the Invention
This invention relates to a simple security device for preventing a door from being opened by the insertion of a key from outside the door. More specifically, this invention relates to a pivotal flap which may be turned to prevent movement of the inside latch knob which controls movement of the dead bolt of the door. Still more specifically, this invention relates to a pivotal flap device which has a spring in the interior thereof which retards accidental turning of the flap to an unsecured position. Still more specifically, this invention relates to a security device which guards against unlocking of a door from the outside by a very simple pivotal flap which is spring guarded against accidental slipping into guarding position. Still more specifically, this invention relates to a security device which is easily and simply attached to existing door locks.
2. State of the Prior Art
There are a number of patents describing various devices for securing door locks from being opened from the outside and from accidental release from such security. These include U.S. Pat. Nos. 192,443; 1,048,784; 3,423,974; 3,748,882; 3,921,423; 4,055,361; 4,152,911; 4,185,483 and 4,279,137. The first three of these patents relate to doors having door knobs on the outside as well as on the inside instead of relying on the insertion of a key from the outside. Moreover these are not dead bolt locks as involved in the present application.
Pat. No. 3,748,882 pertains to a securing device designed for a door lock having a non-circular knob on the inside and describes a complicated securing device for embracing the whole one side of the knob and preventing its turning.
Pat. No. 3,921,423 describes a complicated device for attachment to a dead bolt lock for preventing the turning of the dead bolt control knob. This involves a long sliding bolt and a bracket for holding the sliding bolt therein in and out of contact with the latch knob.
Pat. No. 4,055,361 is a thumb knob assembly that may be substituted for the original thumb knob assembly that comes with the original dead bolt lock. Although this assembly prevents the opening of the lock by a key from the outside, it involves the substantial replacement of the lock assembly.
Pat. No. 4,152,911 discloses an elongated flanged member which is pivotal to an interference and non-interference positions with the bolt moving knob. This is a complicated four-flanged device to embrace the bolt drawing knob for preventing rotation of the same.
Pat. No. 4,185,483 describes the use of six-sided wedge between the door knob handle and the latch which controls the movement of the dead bolt.
Pat. No. 4,279,137 discloses a sliding double bolt device which embraces the latch bolt from both sides and prevents rotation of the same. This represents a complicated structure which needs to be assembled on the door.
None of these patents show the simple device of this invention which may be added to installed door locks by drilling only one hole in the door for a very simple attachment, and the device is very simply designed to avoid accidental locking of the latch knob.